| Known Indirect Subclasses |
A BlockingQueue in which producers may wait for consumers
to receive elements. A TransferQueue may be useful for
example in message passing applications in which producers
sometimes (using method transfer(E)) await receipt of
elements by consumers invoking take or poll, while
at other times enqueue elements (via method put) without
waiting for receipt.
{@linkplain #tryTransfer(Object) Non-blocking} and
{@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
tryTransfer are also available.
A TransferQueue may also be queried, via hasWaitingConsumer(), whether there are any threads waiting for
items, which is a converse analogy to a peek operation.
Like other blocking queues, a TransferQueue may be
capacity bounded. If so, an attempted transfer operation may
initially block waiting for available space, and/or subsequently
block waiting for reception by a consumer. Note that in a queue
with zero capacity, such as SynchronousQueue, put
and transfer are effectively synonymous.
Public Method Summary
| abstract int |
getWaitingConsumerCount()
Returns an estimate of the number of consumers waiting to
receive elements via
BlockingQueue.take() or timed
poll. |
| abstract boolean |
hasWaitingConsumer()
Returns
true if there is at least one consumer waiting
to receive an element via BlockingQueue.take() or
timed poll. |
| abstract void |
transfer(E e)
Transfers the element to a consumer, waiting if necessary to do so.
|
| abstract boolean |
tryTransfer(E e)
Transfers the element to a waiting consumer immediately, if possible.
|
| abstract boolean |
tryTransfer(E e, long timeout, TimeUnit unit)
Transfers the element to a consumer if it is possible to do so
before the timeout elapses.
|
Inherited Method Summary
Public Methods
public abstract int getWaitingConsumerCount ()
Returns an estimate of the number of consumers waiting to
receive elements via BlockingQueue.take() or timed
poll. The return value is an
approximation of a momentary state of affairs, that may be
inaccurate if consumers have completed or given up waiting.
The value may be useful for monitoring and heuristics, but
not for synchronization control. Implementations of this
method are likely to be noticeably slower than those for
hasWaitingConsumer().
Returns
- the number of consumers waiting to receive elements
public abstract boolean hasWaitingConsumer ()
Returns true if there is at least one consumer waiting
to receive an element via BlockingQueue.take() or
timed poll.
The return value represents a momentary state of affairs.
Returns
trueif there is at least one waiting consumer
public abstract void transfer (E e)
Transfers the element to a consumer, waiting if necessary to do so.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
BlockingQueue.take() or timed poll),
else waits until the element is received by a consumer.
Parameters
| e | the element to transfer |
|---|
Throws
| InterruptedException | if interrupted while waiting, in which case the element is not left enqueued |
|---|---|
| ClassCastException | if the class of the specified element prevents it from being added to this queue |
| NullPointerException | if the specified element is null |
| IllegalArgumentException | if some property of the specified element prevents it from being added to this queue |
public abstract boolean tryTransfer (E e)
Transfers the element to a waiting consumer immediately, if possible.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
BlockingQueue.take() or timed poll),
otherwise returning false without enqueuing the element.
Parameters
| e | the element to transfer |
|---|
Returns
trueif the element was transferred, elsefalse
Throws
| ClassCastException | if the class of the specified element prevents it from being added to this queue |
|---|---|
| NullPointerException | if the specified element is null |
| IllegalArgumentException | if some property of the specified element prevents it from being added to this queue |
public abstract boolean tryTransfer (E e, long timeout, TimeUnit unit)
Transfers the element to a consumer if it is possible to do so before the timeout elapses.
More precisely, transfers the specified element immediately
if there exists a consumer already waiting to receive it (in
BlockingQueue.take() or timed poll),
else waits until the element is received by a consumer,
returning false if the specified wait time elapses
before the element can be transferred.
Parameters
| e | the element to transfer |
|---|---|
| timeout | how long to wait before giving up, in units of
unit |
| unit | a TimeUnit determining how to interpret the
timeout parameter |
Returns
trueif successful, orfalseif the specified waiting time elapses before completion, in which case the element is not left enqueued
Throws
| InterruptedException | if interrupted while waiting, in which case the element is not left enqueued |
|---|---|
| ClassCastException | if the class of the specified element prevents it from being added to this queue |
| NullPointerException | if the specified element is null |
| IllegalArgumentException | if some property of the specified element prevents it from being added to this queue |